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A THEORETICAL STUDY OF NORMAL ALKANE COMBUSTION
by
Xiaoqing You
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MECHANICAL ENGINEERING)
August 2008
Copyright 2008 Xiaoqing You

Basic understanding of the combustion kinetics of jet fuels is critical to optimal design of gas-turbine engines. Because jet fuels contain a large number of compounds, a current approach to their combustion kinetics is to use a surrogate, containing several compounds, to mimic jet-fuel behaviors. Towards the goal of developing a combustion kinetic model for jet-fuel surrogates, a theoretical study was undertook here, focusing largely on a particular class of surrogate component, namely, the normal alkanes.; To develop a combustion reaction model for fuel surrogates requires a reliable H2/CO/C1-C4 combustion sub-model as its foundation. Therefore, a significant portion of the current work is to improve H2/CO/C1-C4 high-temperature combustion model through a critical evaluation of rate parameters, theoretical studies for several key reactions, ab initio calculations of thermochemical properties, and validation tests against a wide range of experimental data.; Notably, the kinetics of reactions CO+HO2• → CO2+•OH and •OH+HO2• → H2O+O2 were studied using a combination of ab initio electronic structure methods, transition state and RRKM theories, and master equation modeling. New mathematical formulations and numerical algorithms for treating asymmetric hindered internal rotation were developed. Rate parameters were recommended along with their uncertainty factors.; On the basis of the updated H2/CO/ C1-C4 kinetic model, a detailed kinetic model was proposed for the combustion of normal alkanes up to n-dodecane. The model is valid for fuel oxidation and pyrolysis above 850 K, and was validated against a wide range of experimental data, including fuel pyrolysis in plug flow and jet-stirred reactors, laminar flame speeds, and ignition delay times behind reflected shock waves, with n-heptane, n-decane, and n-dodecane being the emphasis.; Analyses revealed that for a wide range of combustion conditions, the kinetics of fuel cracking to form smaller molecular fragments is fast and may be decoupled from the oxidation kinetics of the fragments. Subsequently, a simplified reaction model containing 4 species and 20 reaction steps was proposed to predict the fuel pyrolysis rate and product distribution. Combined with the base H2/CO/C1-C4 model, the simplified model was shown to predict fuel pyrolysis, laminar flame speeds, and ignition delays as closely as the detailed model.

A THEORETICAL STUDY OF NORMAL ALKANE COMBUSTION
by
Xiaoqing You
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(MECHANICAL ENGINEERING)
August 2008
Copyright 2008 Xiaoqing You